Principles + OOP + UML

For each snippet: name the principle violated, explain why, and write the fixed version.

// Snippet A — which principle?
class Report {
  String generateHTML() { ... }
  String generatePDF() { ... }
  void saveToFile(String path) { ... }
  void uploadToS3() { ... }
  void emailReport(String to) { ... }
}
// Snippet B — which principle?
class Square extends Rectangle {
void setWidth(int w)  { this.width=w; this.height=w; }
void setHeight(int h) { this.width=h; this.height=h; }
}
// Snippet C — which principle?
interface Printable {
void print(); void scan(); void fax(); void copy();
}
class BasicPrinter implements Printable {
void print() { … }
void scan()  { throw new UnsupportedOperationException(); }
void fax()   { throw new UnsupportedOperationException(); }
void copy()  { throw new UnsupportedOperationException(); }
}
// Snippet D — which principle?
class NotificationService {
void notify(String type, String message) {
if (type.equals(“EMAIL”)) sendEmail(message);
else if (type.equals(“SMS”)) sendSMS(message);
else if (type.equals(“PUSH”)) sendPush(message);
}
}

Draw the UML class diagram with these entities. Include all attributes, methods, relationships with correct symbols, and multiplicities.

Entities: Library, Member, Book, BookCopy, Loan, Librarian
Requirements:

A Library has many Members and many BookCopies
A Book can have multiple BookCopies
A Loan connects a Member to a BookCopy (with dates)
A Librarian manages loans
Members have a borrowing limit (max 3 books)
BookCopy has status: AVAILABLE, BORROWED, RESERVED

Include: composition vs aggregation distinction
inheritance if Librarian IS-A Member
all multiplicities on every relationship

Draw a sequence diagram for the complete order placement flow including the failure path.

Actors: Customer, OrderService, PaymentService,
        InventoryService, EmailService
Happy path:

Customer → OrderService: placeOrder(cart)
OrderService → PaymentService: validatePayment(card)
PaymentService → OrderService: paymentConfirmed
OrderService → InventoryService: reserveItems(cart)
InventoryService → OrderService: reservationId
OrderService → EmailService: sendConfirmation(email)
OrderService → Customer: orderId

Also model: what happens when payment fails?
Show the failure path as an alt block

The violating code below has multiple SOLID violations. List every violation with line references, produce refactored Java code, and draw the UML class diagram of your solution.

class ParkingLot {
  private int totalSpots = 100;
  private int occupiedSpots = 0;
  private List<String[]> parkedVehicles = new ArrayList<>();
public String parkVehicle(String vehicleType, String plate) {
if (occupiedSpots >= totalSpots) return “Lot is full”;
// ← VIOLATION: what principle? why?
double rate;
if (vehicleType.equals("CAR"))   rate = 20.0;
else if (vehicleType.equals("BIKE"))  rate = 10.0;
else if (vehicleType.equals("TRUCK")) rate = 40.0;
else return "Unknown vehicle type";

// ← VIOLATION: what principle? why?
String ticketId = "T" + System.currentTimeMillis();
parkedVehicles.add(new String[]{ticketId, plate,
  vehicleType, String.valueOf(System.currentTimeMillis()),
  String.valueOf(rate)});
occupiedSpots++;

// ← VIOLATION: what principle? why?
System.out.println("Parked " + vehicleType);

// ← VIOLATION: what principle? why?
saveToDatabase(ticketId, plate);
return ticketId;
}
private void saveToDatabase(String id, String plate) {
System.out.println(“Saving to MySQL: ” + id);  // hardcoded!
}
public double calculateBill(String ticketId) {
// billing logic crammed here ← VIOLATION: what principle?
for (String[] v : parkedVehicles) {
if (v[0].equals(ticketId)) {
long entry = Long.parseLong(v[3]);
double hours = (System.currentTimeMillis()-entry)/3600000.0;
double rate  = Double.parseDouble(v[4]);
return Math.ceil(hours) * rate;
}
}
return 0;
}
}
Deliverable:

List each violation (principle + explanation)
Refactored Java code (multiple classes)
UML class diagram of the refactored design